1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device such as a thin film transistor.
2. Description of the Prior Art
A thin film transistor (hereinafter referred to as a polycrystalline silicon TFT) employing a polycrystalline silicon film formed on a transparent insulating substrate as an active layer is recently employed as a pixel drive element (pixel drive transistor) for a commercially available active matrix liquid crystal display (LCD).
Such a polycrystalline silicon TFT advantageously has larger mobility and higher drivability than a thin film transistor employing an amorphous silicon film as an active layer. Therefore, an LCD of high performance can be implemented with the polycrystalline silicon TFT. Further, the polycrystalline silicon TFT having high drivability is also employable for a peripheral drive circuit (driver part). When employing the polycrystalline silicon TFT, therefore, an LCD of high performance can be implemented while not only a pixel part (display part) but also a peripheral drive circuit (driver part) can be integrally formed on the same substrate.
In such a polycrystalline silicon TFT, the polycrystalline silicon film serving as the active layer is formed by directly depositing a polycrystalline silicon film on a substrate or forming an amorphous silicon film on a substrate and thereafter polycrystallizing the same. The former method has a relatively simple step of directly depositing the polycrystalline silicon film on the substrate by CVD under a high temperature.
In the latter method, the deposited amorphous silicon film is generally polycrystallized by a solid phase growth method. According to this solid phase growth method, the amorphous silicon film is heat treated to be polycrystallized in the solid state, for obtaining the polycrystalline silicon film.
This solid phase growth method is referred to as a high-temperature process due to employment of a high temperature of about 900xc2x0 C. for activating an impurity or the like, and advantageously requires only a short treatment time when employing a heat-resistant substrate (e.g., a quartz substrate).
However, the aforementioned heat-resistant substrate is high-priced while a relatively low-priced glass substrate is disadvantageously thermally distorted. In recent years, therefore, a low-temperature process enabling employment of the low-priced glass substrate is actively developed.
In particular, a TFT serving as a drive must indispensably be improved in performance, and is subjected to various approaches such as improvement in quality of materials forming the TFT through the low-temperature process.
As a technique of improving the quality of an active layer material influencing the device characteristics, for example, there is developed a technique of forming a polycrystalline silicon film by performing excimer laser annealing on a starting material of an amorphous silicon film.
In general, however, it is difficult to homogeneously perform laser annealing since absorptivity is remarkably influenced by the thickness or the quality of the annealed semiconductor film. Therefore, element characteristics are disadvantageously dispersed to reduce the yield. Particularly when employing a pulse oscillation laser, the element characteristics are remarkably dispersed due to dispersion of the beam intensity resulting from instable pulse oscillation.
An object of the present invention is to provide a method of fabricating a semiconductor device capable of fabricating a semiconductor device including a polycrystalline silicon film having excellent characteristics with a high yield.
Another object of the present invention is to allow employment of a low-priced substrate by enabling a low-temperature process in the aforementioned method of fabricating a semiconductor device.
A method of fabricating a semiconductor device according to an aspect of the present invention comprises a first step of forming a first amorphous semiconductor film on a substrate, a second step of forming a conductive film on the first amorphous semiconductor film, a third step of irradiating the conductive film with an electromagnetic wave thereby making the conductive film generate heat and converting the first amorphous semiconductor film to a first polycrystalline semiconductor film through the heat and a fourth step of thereafter working the conductive film into a gate electrode.
In the method of fabricating a semiconductor device according to this aspect, polycrystallization is homogeneously performed with no dispersion through the heat from the conductive film irradiated with the electromagnetic wave as described above. Consequently, an excellent first polycrystalline silicon film can be formed with an excellent yield. The conductive film is worked into the gate electrode, whereby the fabrication process can be simplified as compared with the case of newly forming the gate electrode after removing the conductive film.
Preferably, the method of fabricating a semiconductor device according to this aspect irradiates the conductive film with the electromagnetic wave and makes the conductive film generate heat for a short time and at a high temperature respectively. When treating the conductive film at a high temperature for a short time in the aforementioned manner, the so-called low-temperature process allowing employment of a low-priced substrate having low heat resistance can be employed.
In the method of fabricating a semiconductor device according to this aspect, the conductive film may include a metal film. Alternatively, the conductive film may include a multilayer structure of a metal film and a second amorphous semiconductor film located under the metal film. In this case, the method of fabricating a semiconductor device preferably converts the second amorphous semiconductor film to a second polycrystalline semiconductor film in the third step. Preferably, the electromagnetic wave includes any of a high-frequency wave, a continuous oscillation laser beam and a lamp beam.
The method of fabricating a semiconductor device according to this aspect preferably further comprises a step of forming an insulator film on the first amorphous semiconductor film before the second step. Preferably, the method of fabricating a semiconductor device works the conductive film into the gate electrode and forms a transistor having the first polycrystalline semiconductor film as an active layer in the fourth step. In this case, the method of fabricating a semiconductor device preferably forms a source/drain region after working the conductive film into the gate electrode and thereafter performs heat treatment at a high temperature for a short time thereby activating the source/drain region. When activating the source/drain region by such high-temperature short-time treatment, the so-called low-temperature process allowing employment of a low-priced substrate having low heat resistance can be employed.
The method of fabricating a semiconductor device preferably introduces an impurity into the first amorphous semiconductor film thereby forming a source/drain region in advance of the third step and irradiates the conductive film for forming the gate electrode with the electromagnetic wave thereby making the conductive film generate heat and simultaneously performing polycrystallization of the first amorphous semiconductor film into the first polycrystalline semiconductor film and activation of the source/drain region in the third step. Thus, the fabrication process can be simplified as compared with the case of performing polycrystallization and activation of the source/drain region through different steps.
A method of fabricating a semiconductor device according to another aspect of the present invention comprises a first step of forming a first amorphous semiconductor film on a substrate, a second step of forming a conductive film on the first amorphous semiconductor film and a third step of irradiating the conductive film with a high-frequency wave thereby making the conductive film generate heat and converting the first amorphous semiconductor film to a first polycrystalline semiconductor film through the heat. Throughout the specification, the term xe2x80x9chigh-frequency wavexe2x80x9d stands for an electromagnetic wave having a frequency (wavelength) of 100 KHz to 300 GHz (xcex=1 mm to 3000 m).
In the method of fabricating a semiconductor device according to this aspect, polycrystallization is homogeneously performed with no dispersion through the heat from the conductive film irradiated with the high-frequency wave. Consequently, an excellent first polycrystalline silicon film can be formed with a high yield.
The method of fabricating a semiconductor device according to this aspect preferably irradiates the conductive film with the high-frequency wave and makes the conductive film generate heat for a short time and at a high temperature respectively. Thus, the so-called low-temperature process allowing employment of a low-priced substrate having low heat resistance can be employed.
In the method of fabricating a semiconductor device according to this aspect, the conductive film may include a metal film. Alternatively, the conductive film may include a multilayer structure of a metal film and a second amorphous semiconductor film located under the metal film. In this case, the method of fabricating a semiconductor device preferably converts the second amorphous semiconductor film to a second polycrystalline semiconductor film in the third step.
The method of fabricating a semiconductor device according to this aspect preferably further comprises a step of forming an insulator film on the first amorphous semiconductor film before the second step. Further, the method of fabricating a semiconductor device preferably works the conductive film into a gate electrode and forms a transistor having the first polycrystalline semiconductor film as an active layer after the third step. Thus, the fabrication process can be simplified as compared with the case of removing the conductive film and thereafter newly forming the gate electrode. In this case, the method of fabricating a semiconductor device preferably forms a source/drain region after working the conductive film into the gate electrode and thereafter performs heat treatment at a high temperature for a short time thereby activating the source/drain region. Thus, the so-called low-temperature process allowing employment of a low-priced substrate having low heat resistance can be employed.
A method of fabricating a semiconductor device according to still another aspect of the present invention comprises a first step of forming a first amorphous semiconductor film on a substrate, a second step of forming a conductive film on the first amorphous semiconductor film and a third step of irradiating the conductive film with a continuous oscillation laser beam thereby making the conductive film generate heat and converting the first amorphous semiconductor film to a first polycrystalline semiconductor film through the heat.
In the method of fabricating a semiconductor device according to this aspect, the continuous oscillation laser beam having homogeneous beam intensity dissimilarly to a pulse laser beam is so employed as to homogeneously perform polycrystallization with no dispersion. Thus, dispersion of element characteristics can be reduced for improving the yield as a result.
The method of fabricating a semiconductor device according to this aspect preferably irradiates the conductive film with the continuous oscillation laser beam and makes the conductive film generate heat for a short time and at a high temperature respectively. Thus, the so-called low-temperature process allowing employment of a low-priced substrate having low heat resistance can be employed.
In the method of fabricating a semiconductor device according to this aspect, the conductive film may include a metal film. Alternatively, the conductive film may include a multilayer structure of a metal film and a second amorphous semiconductor film located under the metal film. In this case, the method of fabricating a semiconductor device preferably converts the second amorphous semiconductor film to a second polycrystalline semiconductor film in the third step.
The method of fabricating a semiconductor device according to this aspect preferably further comprises a step of forming an insulator film on the first amorphous semiconductor film before the second step. Further, the method of fabricating a semiconductor device preferably works the conductive film into a gate electrode and forms a transistor having the first polycrystalline semiconductor film as an active layer after the third step. Thus, the fabrication process can be simplified as compared with the case of newly forming the gate electrode after removing the conductive film. In this case, the method of fabricating a semiconductor device preferably forms a source/drain region after working the conductive film into the gate electrode and thereafter performs heat treatment at a high temperature for a short time thereby activating the source/drain region. Thus, the so-called low-temperature process allowing employment of a low-priced substrate having low heat resistance can be employed.
The method of fabricating a semiconductor device according to this aspect preferably works the conductive film into a gate electrode after the third step, introduces an impurity into the first amorphous semiconductor film thereby forming a source/drain region in advance of the third step, and irradiates the conductive film for forming the gate electrode with the continuous oscillation laser beam thereby making the conductive film generate heat and simultaneously performing polycrystallization of the first amorphous semiconductor film into the first polycrystalline semiconductor film and activation of the source/drain region in the third step. Thus, the fabrication process can be simplified as compared with the case of performing polycrystallization and activation of the source/drain region through different steps. Further, the conductive film is so worked into the gate electrode that the fabrication process can be simplified as compared with the case of newly forming the gate electrode after removing the conductive film.
The method of fabricating a semiconductor device according to this aspect preferably works the conductive film into a shading film after the third step, introduces an impurity into the first amorphous semiconductor film thereby forming a source/drain region in advance of the third step, and irradiates the conductive film for forming the shading film with the continuous oscillation laser beam thereby making the conductive film generate heat and simultaneously performing polycrystallization of the first amorphous semiconductor film into the first polycrystalline semiconductor film and activation of the source/drain region in the third step. Thus, the fabrication process can be simplified as compared with the case of performing polycrystallization and activation of the source/drain region through different steps. Further, the conductive film is worked into the shading film, whereby the fabrication process can be simplified as compared with the case of newly forming the shading film after removing the conductive film.
The method of fabricating a semiconductor device according to this aspect preferably works the conductive film into a source/drain wire after the third step, introduces an impurity into the first amorphous semiconductor film thereby forming a source/drain region in advance of the third step, and irradiates the conductive film for forming the source/drain wire with the continuous oscillation laser beam thereby making the conductive film generate heat and simultaneously performing polycrystallization of the first amorphous semiconductor film into the first polycrystalline semiconductor film and activation of the source/drain region in the third step. Thus, the fabrication process can be simplified as compared with the case of performing polycrystallization and activation of the source/drain region through different steps. Further, the conductive film is so worked into the source/drain wire that the fabrication process can be simplified as compared with the case of newly forming the source/drain wire after removing the conductive film.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.